JP3770428B2 - Integrated semiconductor laser device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an integrated semiconductor laser element that can be used for optical communication and the like, and a manufacturing method thereof, and more particularly to an integrated semiconductor laser integrally formed with an optical waveguide and a manufacturing method thereof.
[0002]
[Prior art]
Conventionally, in an integrated semiconductor laser device, when realizing a monolithic optical integrated circuit, it is important to integrally form a semiconductor laser device and a low-loss optical waveguide from the viewpoint of coupling efficiency as well as from the viewpoint of device manufacturing yield. is there. As a conventional integrated semiconductor laser element, in 1989, R.A. Azoulay et al., Applied Physics Letters, vol. 54, pp 1857 to 1858, an integrally molded one has been proposed. FIG. 9 shows a cross-sectional view of an example of a conventional butt-coupled integrated semiconductor laser device. An optical waveguide 310, an n-type cladding layer 320, an active layer 330, and a P-type cladding layer 340 are stacked in this order on a stepped substrate 300.
[0003]
As described above, the active layer 330 and the optical waveguide 310 are monolithically formed by metal organic chemical vapor deposition (MOCVD) using the step of the substrate. In FIG. 8, the laser light generated in the active layer 330 is propagated to the optical waveguide 310.
[0004]
[Problems to be solved by the invention]
However, the conventional example has the following drawbacks.
[0005]
Since the n-type cladding layer 320 (about 2 μm) exists between the active layer 330 and the optical waveguide 310 in the stepped portion, when light propagates, the light is absorbed by the n-type cladding layer 320 and light of about 1 dB. Waveguide loss occurs.
[0006]
In addition, it is difficult to accurately match the heights of the active layer 330 and the optical waveguide 310 by MOCVD, in actual manufacturing of a semiconductor laser device, and degradation of coupling efficiency is inevitable. For example, when the height of the active layer 330 and the optical waveguide 310 is shifted by ± 0.2 μm, an optical waveguide loss of about 1.5 dB occurs.
[0007]
Also, a method of forming an integrated type integrated semiconductor laser element by forming a semiconductor laser including an active layer in the first growth and separately forming optical waveguides made of semiconductor in the second growth is also considered. It is done. However, in the case of such regrowth, the first growth condition and the second regrowth condition are not necessarily the same. For this reason, the thickness of the optical waveguide may deviate from the design value, and the active layer may not match the height of the optical waveguide. Therefore, there is a problem that the coupling efficiency is deteriorated.
[0008]
Therefore, the present invention has been made to solve the above problems, and can easily align the laser emission position of the semiconductor laser element and the optical waveguide, and has an integrated type having high coupling efficiency. An object of the present invention is to provide a semiconductor laser element.
[0009]
[Means for Solving the Problems]
In an integrated semiconductor laser device in which a semiconductor laser portion having an active layer and an optical waveguide portion of the present invention are provided on the same semiconductor substrate, the optical waveguide portion has a hollow structure surrounded by a wall surface made of a semiconductor, and the optical waveguide The waveguide portion is formed directly on the laser light emitting end face of the semiconductor laser portion.
[0010]
The inner surface of the hollow structure of the optical waveguide portion is covered with metal.
[0011]
Furthermore, the hollow structure of the optical waveguide part is embedded with a material whose refractive index is equal to or lower than the refractive index of the semiconductor on the wall surface of the optical waveguide.
[0012]
Further, in the method of manufacturing an integrated semiconductor laser device, a step of stacking a semiconductor for forming a semiconductor laser portion having an active layer, and a step of forming a hollow structure of an optical waveguide portion by etching a part of the stacked semiconductor And a step of placing a substrate made of a semiconductor on the upper surface of the substantially vertical recess formed by the etching.
[0013]
Further, the step of laminating the semiconductor is a step of laminating a semiconductor for forming an etching stop layer on a substrate and forming a semiconductor laser part having an active layer thereon, and the step of forming the hollow structure The etching is performed to the depth of the etching stopper layer.
[0014]
In addition, a semiconductor forming the semiconductor laser portion is laminated so that the active layer is positioned substantially at the center of the hollow structure of the optical waveguide portion.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 is an example of the case where the present invention is used for an integrated semiconductor laser device for optical communication, and more specifically, is a perspective view of an integrated semiconductor laser device for transmission for Fiber To The Home (FTTH). . In the semiconductor laser section, an n-AlAs etch stop layer 108, an n-AlGaAs cladding layer 101, an AlGaAs active layer 102, and a p-AlGaAs first cladding layer 103 are stacked on a (100) plane n-GaAs substrate 100, A diffraction grating is formed from the p-AlGaAs guide layer 104 and the p-GaAs absorption layer 105 thereon. A p-AlGaAs second cladding layer 106 and a p-GaAs contact layer 107 are stacked thereon.
[0016]
The optical waveguide portion is a hollow optical waveguide having a bottom surface composed of an n-GaAs substrate 100 and an n-AlAs etch stop layer 108, a side surface composed of a laminated structure of semiconductors, and an upper surface composed of a wall surface composed of a GaAs substrate 141. .
[0017]
The integrated semiconductor laser device of the present invention has a structure in which a semiconductor laser portion and an optical waveguide portion are directly coupled. In addition, the active layer and the optical waveguide are designed so that their heights match each other, i.e., approximately at the center of the optical waveguide. The size of the optical waveguide is appropriately selected according to design conditions such as material and refractive index. Here, the size of the optical waveguide is 1 μm deep, 4 μm wide, and 100 μm long.
[0018]
Next, the manufacturing process of the integrated semiconductor laser device of the present invention will be described. First, an n-AlAs etch stop layer 108 having a thickness of 0.1 nm, an n-AlGaAs cladding layer 101 having a thickness of 1.0 μm, and an AlGaAs active layer 102 having a thickness of 0.08 μm are formed on the (100) plane n-GaAs substrate 100 by MOCVD. The p-AlGaAs first cladding layer 103 having a thickness of 0.2 μm, the p-AlGaAs guide layer 104 having a thickness of 0.15 μm, and the p-GaAs absorption layer 105 having a thickness of 0.06 μm are continuously grown. A perspective view after the process thus formed is shown in FIG.
[0019]
Next, the diffraction grating 120 having a period of about 0.36 nm and a depth of about 0.18 μm is imprinted on the wafer by using a normal two-beam interference exposure method and a wet etching method. The diffraction grating 120 functions as a third-order diffraction grating for laser light having a wavelength of 780 nm. A perspective view after the process thus formed is shown in FIG.
[0020]
Subsequently, a 0.39 μm thick p-AlGaAs second cladding layer 106 and a 0.3 μm thick p-GaAs contact layer 107 are grown on the wafer having the diffraction grating 120 by using the MOCVD method. A perspective view after the process thus formed is shown in FIG.
[0021]
Next, the dielectric film 130 is processed into a mask by a normal photolithography technique, and etching is performed up to the etch stop layer 108 by using a reactive ion etching technique with the dielectric film 130 as a mask.
[0022]
By this etching, the depth of the optical waveguide is uniformly formed. A substantially vertical recess 131 having a depth of 1 μm and a width of 4 μm is formed in a part of the wafer. In this step, the active layer is automatically positioned at the center in the depth direction of the substantially vertical recess 131. A perspective view after the process thus formed is shown in FIG.
[0023]
Next, the dielectric film 130 is removed. The dielectric film 133 is applied, and the ridge portion of the laser portion 132 and the solder material reservoir 135 are formed using a normal photolithography technique and a reactive ion etching technique using the dielectric film 133 as a mask. A perspective view after the process thus formed is shown in FIG.
[0024]
Next, the dielectric film 133 is removed. A perspective view after the process thus formed is shown in FIG. Next, the GaAs substrate 141 is overlaid so as to face the contact layer 107, soldered with an AuSn solder material injected into the solder material reservoir 135, and finally the substrate is divided into chips by a cleavage method. Get the element. At this time, excess solder material flows out through a groove provided in the solder material reservoir 135, the GaAs substrate 141 and the contact layer 107 are in close contact with each other, and no height shift occurs. A perspective view after the step thus formed is shown in FIG.
[0025]
The integrated semiconductor laser of the present embodiment is coupled directly to the hollow optical waveguide from the emitting end face of the laser having the active layer of 0.08 μm, so that there is no unnecessary layer between the active layer and the optical waveguide, And since there is almost no deviation in height, there is no coupling loss due to the influence. In other words, compared to the conventional example, there is no loss between the active layer and the optical waveguide (approximately 2 μm), resulting in a loss of 1 dB, and further, there is no height shift (approximately ± 0.2 μm), resulting in a loss of 1.5 dB. Get away.
[0026]
The feature of the integrated semiconductor laser device of the present invention is that the laser part and the optical waveguide part are directly joined in the process of manufacturing the element, so that the connectivity is good, and the height of the optical waveguide and the active layer is not shifted. Since a hollow optical waveguide is employed, it is easy to branch and multiplex light in the optical waveguide portion.
[0027]
(Example 2)
Next, a method for manufacturing an integrated semiconductor laser device for optical communication in the case where a metal vapor deposition film is present inside the optical waveguide will be described. First, the process up to the step of FIG. Next, in order to prevent the deposition of Au, the semiconductor laser part 132 is covered with a shielding material such as a GaAs substrate and Au is deposited on the surface of the substantially vertical recess by oblique vacuum deposition so that the Au is not deposited on the laser emission surface. Evaporation is performed to form an Au vapor deposition film 140 with a thickness of 100 nm covering the inner surface of the substantially vertical recess. A perspective view after the process thus formed is shown in FIG.
[0028]
FIG. 7 is a detailed perspective view of a substantially vertical recess. The angle at the time of vapor deposition is demonstrated easily using this figure. It suffices that the metal is vapor-deposited at least in the region where the light spreading direction 450 from the emission end face of the active layer 430 is irradiated to the inner surface of the optical waveguide.
[0029]
From this, the relational expression established between the light spreading angle 420 (this angle is α) and the vapor deposition angle 410 (this angle is β) is:
tan α × tan β = 1/2
It becomes. Since the light divergence angle is determined by the structure of the semiconductor laser, it is generally in a range satisfying 0 to β, that is, in a direction greater than 0 and less than tan ⁻¹ (1 / (2 × tan α)). Vapor deposition is performed. Since α = 45 degrees in this embodiment, the deposition direction 440 is performed with the deposition angle 440 being 45 degrees or less.
[0030]
Next, Au is vapor-deposited on the GaAs substrate 141 to form an Au vapor-deposited film 142 having a thickness of 100 nm. However, the material to be deposited is not limited to Au. A perspective view in this step is shown in FIG.
[0031]
Then, the AuSn solder material that is superposed on the Au vapor deposition film 140 of the integrated semiconductor laser element so that the Au vapor deposition film 140 and the Au vapor deposition film 142 on the surfaces of both substrates face each other and is injected into the solder material reservoir 135. Then, the two substrates are finally divided into chips by a cleavage method to obtain an integrated semiconductor laser device. A perspective view after this step is shown in FIG. At this time, the excess solder material flows out through a groove provided in the solder material reservoir 135, and the Au vapor deposition film 140 and the Au vapor deposition film 142 are in close contact with each other, so that no height deviation occurs.
[0032]
Further, as in the first embodiment, coupling loss does not occur because the laser beam is directly coupled to the optical waveguide from the laser emission end face. Furthermore, since an Au vapor deposition film is formed, although depending on the refractive index of the material used, the propagation loss of the metal clad optical waveguide when using Au as in this embodiment is the propagation loss of the semiconductor clad optical waveguide. In this case, it is about 1/100. In this embodiment, an Au vapor deposition film is formed, but other metals may be used.
[0033]
Example 3
FIG. 8 is a perspective view of an integrated semiconductor laser device for optical communication when the material is embedded in the optical waveguide of the hollow structure portion with the same configuration as that of the integrated semiconductor laser device as in the second embodiment.
[0034]
Next, a method for manufacturing an integrated semiconductor laser device will be briefly described. First, a substantially vertical recess 131 is formed by performing the process up to the step of FIG. 3D in the same manner as in Example 1, and then Au is evaporated inside the optical waveguide. Next, the substantially vertical recess 131 is filled with polyimide 209, and only the excessively adhered polyimide is removed by ashing to adjust the height. A perspective view after the process thus formed is shown in FIG.
[0035]
Then, an optical waveguide is formed by depositing an Au vapor deposition film 208 on the upper surface. A perspective view after the process thus formed is shown in FIG.
[0036]
Thereafter, the integrated semiconductor laser device is cut out by the cleavage method in the same manner as in the first and second embodiments. In this case, since the polyimide (refractive index n = 1.6) exists in the hollow structure portion, chips do not enter the optical waveguide.
[0037]
In the third embodiment, as in the first and second embodiments, since it is directly coupled to the optical waveguide from the laser emission end face, there is no deviation in height compared to the conventional example, so that a loss of 1.5 dB is avoided. In addition, since there is no unnecessary layer between the optical waveguide and the active layer, a loss of 1 dB is avoided. In addition, since the polyimide is embedded in the optical waveguide portion, the reflectivity with the clad is improved, the waveguide loss in the optical waveguide can be suppressed to half or less, and further, the solder material reservoir can be manufactured. Since it is unnecessary, the device is easier to manufacture than in the second embodiment.
[0038]
Note that the material to be embedded is not limited to polyimide. If the material is embedded with a material having a higher refractive index, propagation loss can be reduced. For example, in an optical waveguide embedded with a material having a refractive index n = 3, the propagation loss can be reduced to 1/10 compared to an optical waveguide having a hollow structure (refractive index n = 1). Further, any material may be used as long as it is a material having a smaller refractive index than the semiconductor used for the side wall of the optical waveguide and does not absorb the emission wavelength.
[0039]
【The invention's effect】
According to the present invention, an integrated semiconductor laser device having good connectivity can be obtained because the laser portion and the optical waveguide portion are directly joined in the process of manufacturing the integrated semiconductor laser device. There is no loss of light between the laser portion and the optical waveguide due to the height shift in the manufacturing process. Thereby, the coupling loss when the optical waveguide layer and the active layer are displaced in height can be suppressed.
[0040]
Further, since the metal vapor deposition film is used on the inner surface of the hollow structure of the optical waveguide, the propagation loss of the metal clad optical waveguide can be significantly reduced than the propagation loss of the semiconductor clad optical waveguide.
[0041]
Furthermore, by using a hollow structure filling material, the reflectivity between the filling material and the metal cladding is improved, so that the waveguide loss in the optical waveguide can be reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view of an integrated semiconductor laser device according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a production sequence process in Example 1 of the present invention.
FIG. 3 is a diagram showing a production sequence process in Example 1 of the present invention.
FIG. 4 is a diagram showing a production sequence process in Example 1 of the present invention.
FIG. 5 is a diagram showing a production sequence process in Example 2 of the present invention.
FIG. 6 is a diagram showing a production sequence process in Example 2 of the present invention.
FIG. 7 is a view for explaining an Au vapor deposition angle in Example 2 of the invention.
FIG. 8 is a diagram showing a production sequence process in Example 3 of the invention.
FIG. 9 is a diagram showing a conventional integrated semiconductor laser device.
[Explanation of symbols]
100, 200 n-GaAs substrate 101, 201 n-AlGaAs cladding layer 102, 202 AlGaAs active layer 103, 203 p-AlGaAs first cladding layer 104, 204 p-AlGaAs guide layer 105, 205 p-GaAs absorption layers 106, 206 p-AlGaAs second cladding layer 107, 207 p-GaAs contact layer 108, 210 n-AlAs etch stop layer 120 diffraction grating 130, 133 dielectric film 131 substantially vertical recess 132 semiconductor laser part 135 solder material reservoir 140, 142, 208 Au vapor deposition film 141 GaAs substrate 209 Polyimide 410 Deposition angle 420 Light spread angle 430 Active layer 440 Deposition direction 450 Light spread direction

Claims (6)

In an integrated semiconductor laser device in which a semiconductor laser portion having an active layer and an optical waveguide portion are provided on the same semiconductor substrate,
The optical waveguide part is a hollow structure surrounded by a wall surface made of a semiconductor,
An integrated semiconductor laser device, wherein the optical waveguide portion is directly formed on a laser light emitting end face of the semiconductor laser portion. 2. The integrated semiconductor laser device according to claim 1, wherein an inner surface of the hollow structure of the optical waveguide portion is covered with a metal. 3. The integrated semiconductor laser device according to claim 2, wherein the hollow structure of the optical waveguide portion is embedded with a material having a refractive index equal to or lower than the refractive index of the semiconductor on the wall surface of the optical waveguide. Laminating a semiconductor to form a semiconductor laser part having an active layer;
Etching a part of the laminated semiconductor to form a hollow structure of the optical waveguide part;
And a step of placing a substrate made of a semiconductor on the upper surface of the substantially vertical recess formed by the etching. The step of laminating the semiconductor is a step of laminating a semiconductor that forms an etching stop layer on a substrate and forms a semiconductor laser part having an active layer thereon.
5. The method of manufacturing an integrated semiconductor laser device according to claim 4, wherein the step of forming the hollow structure is a step of etching to the depth of the etching stopper layer. 6. The method of manufacturing an integrated semiconductor laser device according to claim 5, wherein a semiconductor forming the semiconductor laser portion is stacked so that the active layer is positioned substantially at the center of the hollow structure of the optical waveguide portion.

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